The human skin is the largest organ that covers the entire surface of the body. The skin has various functions including temperature control, protection from external environments, etc., and has a surface area of about 1.2 m2 to about 2.3 m2 in adults. The skin is composed of epidermis and dermis. The dermis is composed of collagen and fibroblasts and the epidermis is composed of keratinocytes, melanocytes, etc. Unlike the epidermis, which has a relatively constant thickness, the thickness of the dermis is known to vary greatly depending on the area and is also about 3 times thicker than the epidermis. The epidermis is stratified into sublayers of basement membrane, stratum spinosum, stratum granulosum, and stratum corneum, and many layers of final-differentiated dead cells are amassed on the skin surface to serve a protective function. The basement membrane is in the form of a thin membrane, in which laminin and several extracellular substrates are deposited on a type 4 collagen lattice, and the cells of the stratum basale are attached thereto. Skin damage accompanies decomposition of the basement membrane and allows the cells in the stratum basale to be in contact with type 1 collagen, during which the epidermal cells migrate to the sides, thereby inducing re-epithelialization.
The dermis has many fibroblasts and is composed of papillary dermis (in which microvessels are distributed) and reticular dermis (in which many thick collagen fibers are present). Hair follicles and various auxiliary organs of the skin are located deep in the skin. Accordingly, in a case when the epidermis is lost due to a partial thickness wound, the epidermal cells will grow out of the hair follicles and induce re-epithelialization.
Meanwhile, there have been attempts to constitute artificial skin tissue. Artificial skin can generally be used for replacing damaged skin which has lost its ability to regenerate by self-cells, skin ulcers, or toxicity and efficacy experiments of pharmaceutical drugs or cosmetics, etc. Artificial skin is very important for the development of a skin substitute to replace damaged human skin or a pharmaceutical drug for the treatment thereof, or as an experimental material for toxicity and efficacy tests of a medical device designed to contact with skin, daily essentials, cosmetics, etc.
Accordingly, for such utilization, there is a need for the development of artificial skin having a structure mimicking a natural skin layer. In Europe, the sales of cosmetics manufactured through animal experiments have been completely prohibited since 2013, and thus leading global cosmetics companies are making a heavy investment on the development of artificial skin. For example, Episkin®, self-developed by L'Oreal France, has passed the European Standard for artificial skin, being acknowledged as an artificial skin to completely replace animal experiments, and EpiDerm®, developed by MatTek Corporation in the USA, has acquired only a provisional approval because it shows excessive reaction to human skin. Examples of the representative methods for preparing artificially cultured skin models developed so far may include: a method for preparing reconstructed epidermis on de-epidermized dermis (RE-DED), in which human keratinocytes are cultured three-dimensionally on the dermis where the epidermis is removed; and a method of living skin equivalent (LSE), in which human keratinocytes are cultured on a collagen substrate containing fibroblasts.
However, the three-dimensionally cultured skins developed so far have disadvantages in that a basement membrane is not fully formed between the dermis prepared with collagen and the epidermis and that dermal contraction takes place during the culture process. Therefore, there is still a need for a technology for preparing a three-dimensionally cultured skin that can more closely mimic human skin.